The present invention relates to the art of semiconductor integrated circuit arrangement fabrication, and particularly to an art for dry-etching a thin film on a semiconductor wafer by using radicals or ions in a plasma.
A silicon oxide film, which is a typical insulating film used to fabricate an LSI, is normally processed by a dry-etching system (plasma etching system) using a plasma process.
In the case of an etching process using a typical magneto-microwave plasma etching system, a vacuum chamber of the etching system comprising a reaction chamber (etching chamber) and a discharge chamber is first evacuated up to approx. 10.sup.-6 Torr by an evacuating system and then a reaction gas is introduced into the vacuum chamber through a needle valve to a predetermined pressure (approx. 10.sup.-5 to 10.sup.-1 Torr).
The etching of a silicon oxide film deposited on a silicon wafer uses, for example, a fluorocarbon gas such as CF.sub.4, C.sub.2 F.sub.6, C.sub.3 F.sub.8, or C.sub.4 F.sub.8 and a hydrogen-containing fluorocarbon gas such as CHF.sub.3 or CH.sub.2 F.sub.2, or a mixed gas of a fluorocarbon-based gas and hydrogen. Hereafter, these gases are generally referred to as flon gases.
Microwaves of 1 to 10 GHz (ordinarily of 2.45 GHz) generated by a microwave generator (ordinarily a magnetron) are propagated through a wave guide and are introduced into a discharge tube forming a discharge chamber. The discharge tube is made of an insulating material (ordinarily quartz or alumina) in order to pass microwaves.
A magnetic field is locally formed in the discharge and reaction chambers by an electromagnet and a permanent magnet. When a microwave electric field is introduced into the discharge chamber under the above state, magnetic-field microwave discharge occurs due to a synergistic action between the magnetic field and the microwave electric field, and a plasma is formed.
In this case, the reaction gas dissociates in the plasma and thereby various radicals and ions are generated. Dissociation of the reaction gas is caused because electrons in reaction gas molecules collide with those in the plasma or absorb light, and thereby become excited to antibonding orbitals. These dissociated species are supplied to the surface of a silicon oxide film to participate in the etching of the silicon oxide film while dissociation species influence the dry-etching characteristics in a complex way.
A dry etching system using this type of plasma process is disclosed in Japanese Patent Laid-Open No. 109728/1991.